The power system which is powered by a chargeable battery and the electricity storage system which stores electric energy in a chargeable battery have high requirements on battery consistency and battery lifecycle. The power system and the electricity storage system basically have following requirements: (1) high battery consistency, (2) with limited divergence increasing of batteries after long time operation (such as 8-20 years), (3) preference of battery having high battery capacity for lengthening battery lifecycle, and (4) reducing voltage loss which comes from converting a single input voltage into multiple output voltages.
To meet requirement (1), battery cells are graded to select high quality battery, but the system cost will increase. As for requirement (2), by current technology, it is not easy to meet requirement (2) because the battery divergence is worse after long usage. As for requirement (3), the aged batteries still may have 70% residual battery capacity, but such aged batteries may be replaced for the sake of security. As for requirement (4), currently most systems are suffered by this problem which is not easily to be addressed.
Therefore, a battery system and a control method thereof are needed.